The present invention relates to improved conveyance systems for use in the processing of evacuated articles and, more particularly to individual vehicles for use in such systems.
In the production of television picture tubes or other forms of similar tubes, it is generally necessary in a final process stage to evacuate the tube to a residual pressure of less than about 10.sup.-6 mbar whilst allowing for the tube to be heated during at least some of the process stages.
In a typical production line, each tube is mounted on to an individual conveyance vehicle (sometimes referred to as a "cart") with a plurality of such vehicles forming part of a conveyance system in which the vehicles are in slow but continuous motion along straight or circular/oval production lines. Each conveyance system can typically comprise up to two hundred and fifty vehicles with a production line time of, for example, seventy to one hundred minutes (or more depending on the article being processed.)
Each vehicle generally incorporates equipment required to carry out the various finishing process stages for the picture tubes. The known vehicles generally possess a vacuum system in the form, for example, of a diffusion pump or turbomolecular pump backed by a rotary pump.
The known vehicles conventionally possess a gripper assembly including a seal for receiving the "neck" of the television tube and sealingly connecting the interior of the tube to the vacuum system for maintaining a vacuum therein.
However, in order to inhibit degradation of the seal during subsequent heating of the television tube it is known to use water cooling to effect cooling of the gripper assembly and in particular the seal.
The use of water cooling with moving vehicles is complicated and gives rise to maintenance problems and low reliability.
It is an aim of the present invention to provide a conveyance vehicle for the transportation of a vessel to be evacuated in which the use of a water cooling system is avoided.